Modeling and optimization of an integrated magnetohydrodynamic–magnetophoretic electrochemical reactor for low-energy deionization from brackish water

Abstract

Electrochemical water treatment technologies are increasingly investigated as sustainable and chemical-free alternatives for low-salinity desalination and water softening. However, many systems remain energy intensive or insufficiently optimized. This study revealed the modeling, experimental evaluation, and optimization of an integrated electrochemical–magnetic reactor and integrated magnetohydrodynamic (MHD, Lorentz force) and magnetophoretic (MP, Kelvin force) effects for ion removal from brackish water. The aims were to (i) model the coupled electromagnetic forces, (ii) optimize operational parameters using Central Composite Design (CCD) and Response Surface Methodology (RSM), and (iii) evaluate both removal efficiency and specific energy consumption. A total of 181 experimental runs were conducted by varying salt concentration (≤ 2.5 g/L NaCl equivalent), flow rate, electrode spacing, pipe diameter, and magnetic flux density generated by a 1500-turn coil. The removal efficiency of total dissolved solids (TDS), electrical conductivity (EC), and total hardness (TH) was also evaluated. The control experiments were performed to decouple MHD-only and MP-only contributions. The results demonstrated that the Lorentz force significantly enhanced the ion removal through induced ionic motion and spiral (Larmor-type) trajectories, whereas the Kelvin force alone indicated the ion redistribution and localized concentration gradients. Moreover, the highest performance occurred when both forces acted simultaneously. Under the optimized conditions, the system achieved 64.7% TDS removal, 32.38% EC reduction, and 36.04% hardness removal, with a reactor-level specific energy consumption of 0.0416 kWh/m³. While this removal efficiency is insufficient for single-pass potable standards, the results provided strong potential as a low-energy pre-treatment or multi-stage (cascade) polishing process capable of achieving > 95% removal. Furthermore, MgSO₄ revealed significant magnetic reactivity that was attributed to paramagnetic contributions associated with oxygen-containing species. Although the experiments were conducted using synthetic brackish solutions, the findings provide a mechanistic and statistically optimized framework for magnetic–electrochemical ion separation. Future work should focus on multi-stage reactor integration, validation with real saline waters containing total suspended solids (TSS), organic matter and turbidity, and the evaluation of scale-up energy requirements such as hydraulic and power system losses.